Atrial Fibrillation is the most common disorder of the heart of the heart rhythm requiring medical treatment in the US. It is characterized by an irregular rhythm and excessively fast heart rates, and is thought to affect about 2 million individuals. One common approach to therapy is to use class I or class III anti-arrhythmic drugs to restore and maintain sinus rhythm. An alternative approach is to leave the patient in atrial fibrillation and use digoxin, beta-blockers, or calcium channel blockers to maintain heart rate in the normal range. It is not know whether one approach is preferable to the other with respect to survival and other complications of atrial fibrillation. The NIH initiated this multi-center clinical trial to compare these standard, alternative strategies. The primary objective of the study is to compare whether anti-arrhythmic drug therapy to maintain sinus rhythm has an impact on total mortality when compared to therapy which controls the heart rate in patients with atrial fibrillation. In addition, composite endpoints of disabling stroke, major hemorrhage, and cardiac arrest will be evaluated. Secondary endpoints will be quality of life, functional capacity, mode of death, and hospitalization. Patients will be classified initially by the number of episodes of atrial fibrillation within the past 6 months; single or recurrent episodes. Patients who have a single episode of atrial fibrillation will be randomized only after successful cardioversion (normal sinus rhythm for at least 1 hour). Patients with recurrent episodes of atrial fibrillation will be cardioverted only if they are randomized to rhythm control. When patients are randomized to rhythm control the choice of drugs will be left to the primary treating physician. The anti-arrhythmics include: amiodarone, sotalol, propafenone, flecainide, quinidine, moricizine, disopyramide, and procainamide. AV nodal blocking drugs may also be given. When patients are randomized to heart rate control the choice of drugs will include; beta-blockers, calcium-channel blockers, digoxin, or a combination. In either of the randomization arms, if the drug(s) appears to be successful and does not produce intolerable side effects it will be continued indefinitely. However, if the drug(s) is ineffective or produces intolerable side effects another drug will be given.